1. Field of the Invention
This invention relates to a zigzag sewing machine adapted to form zigzag seams, and more particularly to a safety device in a zigzag sewing machine which prevents various function setting operations from being performed erroneously.
2. Description of the Related Art
In order to form zigzag seams as shown in FIGS. 6(a) to 6(d), a zigzag sewing machine is generally employed which has a so-called "needle swinging mechanism" which swings a sewing needle across the work feed direction.
A zigzag sewing machine of this type has a needle swinging cam for a given seam to be formed. That is, it is provided, as a dedicated sewing machine for forming the seam only, in a sewing factory or the like. For instance, in the case where a so-called "two-dot zigzag seam" as shown in FIG. 6(a) is to be formed, a sewing machine having a needle swinging cam C1 as shown in FIG. 7(a) is provided; and in the case where a so-called "four-dot zigzag seam" as shown in FIG. 6(b) is to be formed, a sewing machine having a needle swinging cam C2 as shown in FIG. 7(b) is provided; and in the case where a so-called "scallop seam" as shown in FIG. 6(c) is to be formed, a sewing machine having a needle swinging cam C3 as shown in FIG. 7(c) is provided.
Those sewing machines are not suitable for the recent apparel industry in which a variety of items are formed each by only a small number.
Hence, it has been proposed to realize a general purpose zigzag sewing machine which has different needle swinging cams, which are replaceable with one another, to form different seams.
In this connection, in order to allow the general purpose zigzag sewing machine to form the different seams which are formed by the dedicated sewing machines, the general purpose zigzag sewing machine should have all the fundamental functions of those dedicated sewing machines.
The fundamental functions of a conventional zigzag sewing machine are a function of adjusting the swing width of the needle swinging mechanism (hereinafter referred to as "a swing width adjusting function", when applicable), a function of changing a seam-forming-position with the position of a needle swing range and a needle swing width set to zero (0) (hereinafter referred to as "a basic line changing function", when applicable), and a function of forming an inverse seam which is axially symmetrical with a normal seam which is formed by an ordinary needle swinging operation (hereinafter referred to as "a seam inverting function", when applicable). Of those functions, the swing width adjusting function is given to all of the dedicated sewing machines; however, the remaining functions, namely, the basic line changing function and the seam inverting function are alternatively given to the dedicated sewing machines according to the kinds of seams they form.
In other words, in the case of the sewing machines which form seams which are each substantially symmetrical with respect to an axis as shown in FIGS. 6(a) and 6(b), it is unnecessary to give the seam inverting function to them, but it is necessary to give the basic line changing function. On the other hand, in the case of the sewing machine which forms a so-called "scallop seam" as shown FIGS. 6(c) and 6(d), the sewing machine must have the seam inverting function, but not the basic line changing function.
Hence, the conventional zigzag sewing machines have only the swing width adjusting function and the basic line changing function, or only the swing width adjusting function and the seam inverting function. That is, there is no conventional zigzag sewing machine which has the three functions.
However, in order to allow a zigzag sewing machine to replace the needle swinging cam to form all the seams shown in FIGS. 6(a) to 6(d), it is essential that the sewing machine has all of the three functions, namely, the swing width adjusting function, the basic line changing line, and the seam inverting function. For this purpose, a zigzag sewing machine as shown in FIGS. 8 and 9 has been proposed in the art.
FIG. 8 shows a conventional zigzag sewing machine M. In the sewing machine M, an electric motor (not shown) is driven to rotate a spindle 2 held by a sewing machine arm Ma and an oscillating shaft (not shown) supported by a sewing machine bed, whereby a sewing needle N is moved up and down, and a sewing machine shuttle is turned. On the other hand, as the sewing machine oscillating shaft turns, a needle swinging cam 4 is turned together with a cam shaft 3, so that a coupling rod 5 with a roller 5a engaged with a cam groove 4a formed in the needle swinging cam 4 moves a needle swinging link 6 up and down which is pivotally coupled to the coupling rod 5.
The needle swinging link 6 is swingably coupled through a coupling shaft 6a to a swing width adjusting link 7 which is so supported that it is swingable about a swing fulcrum shaft 7a. Therefore, the vertical movement of the needle swinging link 6 includes a horizontal component, which is transmitted through a coupling 8 to a swinging rod (or horizontal moving member) 9. One end of the swinging rod 9 is fixedly secured to a needle bar supporting stand 10 which supports a needle bar NL in such a manner that the needle bar NL is vertically movable. As the needle bar supporting stand 10 moves horizontally together with the swinging rod 9, the needle bar NL and accordingly a sewing needle N is swung across the work feed direction.
As was described above, the sewing needle N is moved up and down by the rotation of the sewing machine spindle 2, and swung by the rotation of the sewing machine oscillating shaft, thus forming a zigzag seam as shown in FIGS. 6(a) to 6(d) which turns right and left alternately with respect to the work feed direction. The above-described components 6 through 10 form a needle swinging mechanism A, and the components 4 and 5 and the oscillation shaft (not shown) form driving means.
The above-described needled swinging mechanism A is coupled to a mechanism as shown in FIG. 9, so that the above-described swing width adjusting function, basic line changing function and seam inverting function be realized.
In FIG. 9, reference numeral 11 designates a basic line changing shaft which is swingably supported on a mounting stand Mc which is fixedly secured inside the arm Ma of the sewing machine. A basic line changing knob 12 is fixedly mounted on the outer end portion of the basic line changing shaft 11, and a basic line changing board 13 is fixedly mounted on the inner end portion of the basic line changing shaft 11. Further in FIG. 9, reference numeral 14 designates a swing width adjusting shaft which is fixedly secured to the basic line changing board 13. One end portion of the shaft 14 is inserted into elongated holes Ma1 and Mc1 which are formed in the arm Ma and the mounting stand Mc, respectively, thus being protruded outside the arm Ma. A swing width adjusting knob 15 is fixedly mounted on the outer end portion of the shaft 14. The above-described elongated holes Ma1 and Mc1 are formed arcuate around the basic line changing shaft 11.
Further in FIG. 9, reference numeral 16 designates a swing width adjusting arm. One end of the arm 16 is fixedly connected to the aforementioned swing width adjusting shaft 14, and the other end is connected to the swing fulcrum shaft 7a of the swing width changing link 7.
In the zigzag sewing machine thus organized, the swing width of the sewing needle N is adjusted by turning the swing width adjusting knob 15. That is, as the swing width adjusting knob 15 is turned, the swing width adjusting shaft 14 is turned, so that the swing width adjusting arm 16 and the swing fulcrum shaft 7a are angularly moved about the shaft 14.
Let us consider the case where the swing fulcrum shaft 7a is in a region .alpha. above a horizontal border line Lh passing through the center of the swing width adjusting shaft 4 (hereinafter referred to as "a regular region .alpha.", when applicable). In this case, as the shaft 7a is moved upwardly, the horizontal swing component of the swing width changing link 7 is increased, and the swing width of the sewing needle N is also increased (see FIGS. 10(b) and 10(c)). In contract, as the swing fulcrum shaft 7a located in the regular region .alpha. is moved downwardly towards the horizontal border line Lh, the horizontal swing component of the swing width changing link 7 is decreased, and the swing width of the sewing needle is also decreased. On the other hand, in the case where the swing fulcrum shaft 7a is on the horizontal border line Lh, the horizontal swing component of the swing width changing link 7 is substantially zero as indicated in FIG. 10(a), and the needle swinging operation is stopped. In this case, a straight seam is formed.
Let consider the case where the swing fulcrum shaft 7a is in a region .beta. below the horizontal border line Lh as shown in FIG. 10(d) which is opposite to the region .alpha. (hereinafter referred to as "an inverse region .beta.", when applicable). In this case, as the swing fulcrum shaft 7a is moved downwardly, the horizontal swing component of the needle swinging link 6 is increased, and the swing width of the sewing needle NL is also increased. Let us consider two symmetrical positions above and below the border line Lh. The horizontal components of the swing motions at those two positions are symmetrical, so that the seams formed by the sewing motions are axially symmetrical as shown in FIG. 6(c) or 6(d). That is, if it is assumed that FIG. 6(c) shows a regular seam which is formed with the swing fulcrum shaft 7a set in the regular region .alpha., then FIG. 6(d) shows the seam which is inverse in pattern to the regular seam, being formed with the swing fulcrum shaft 7a set in the inverse region .beta..
The above-described swing width adjusting shaft 14, swing width adjusting knob 15 and swing width adjusting arm 16 form a swing width adjusting mechanism and a pattern changing mechanism.
In the above-described needle swinging operation, the basic line can be changed by turning the basic line changing knob 12.
As the knob 12 is turned, the basic line changing board 13 is turned together with the basic line changing shaft 11, so that the swing width adjusting shaft 14 is moved along the elongated hole Ma1. As a result, the swing width adjusting arm 16 and the swing fulcrum shaft 7a together with the swing width adjusting shaft 14 are swung about the basic line changing shaft 11, and the coupling shaft 6a and the needle swinging link 6 are moved right or left through the swing width changing link 7. This movement is transferred through a coupling 8 to a swing rod 9, so that the sewing needle N is moved right or left. Thus, the basic line has been changed.
That is, as the basic line changing knob 12 is operated, the swing range of the sewing needle is shifted left or right, as a whole, as shown in FIG. 11(b) or 11(c). In the case where the swing width of the sewing needle N is set to zero (0), as shown in FIG. 12(b) or 12(c) the sewing needle N is positioned at the left or right end of the swing range, so that a straight seam is formed there. FIGS. 11(a) and 12(a) show seams which are formed with the basic line set at the middle (center); FIGS. 11(b) and 12(b) show seams which are formed with the basic line set on the left side; and FIGS. 11(c) and 12(c) show seams which are formed with the basic line set on the right side.
Thus, the above-described basic line changing shaft 11, basic line changing knob 12, and basic line changing board 13 form a basic line setting mechanism.
As is apparent from the above description, the conventional zigzag sewing machine has the swing width adjusting function, the inverse seam forming function, and the basic line changing function, thus being able to form a variety of seams.
However, the above-described conventional zigzag sewing machine is disadvantageous in the following points:
With the sewing machine, under the condition that a basic line other than the middle basic line is set, an inverse pattern sewing mode may be set. If, under this condition, the sewing operation is carried out, the sewing needle N may interfere with the throat plate, or the resultant seam may be unacceptable.
In the case where the middle basic line is selected, the swing width adjusting shaft 14 is positioned on the border line Lh as shown in FIG. 13(a). Hence, even if the swing fulcrum shaft 7a is shifted from a regular pattern setting position to an inverse pattern setting position by turning the swing width adjusting arm 16, the position of the shaft 7a is maintained unchanged in a horizontal direction as shown in FIG. 13(a) (being on the line P1), and therefore the swing range of the sewing needle N is not changed as shown in FIGS. 13(b) and 13(c). That is, the sewing needle N is allowed to swing while being regulated by a needle drop hole NB1 formed in the throat plate NB.
On the other hand, the left or right basic line may be selected as shown in FIG. 14(a) or 15(a). In this case, as indicated by reference characters P1 and P2 in FIGS. 14(a) and 15(a) the position of the swing fulcrum shaft 7a in a horizontal direction in the case where a regular pattern sewing mode is set (as indicated by the solid lines) is different from that of the shaft 7a in the horizontal direction in the case where an inverse pattern sewing mode is set (as indicated by the one-dot chain lines). Hence, in the case where the left basic line or the right basis line is set, the swing ranges of the needle swinging link and the sewing needle are shifted, as a result of which the sewing needle interferes with the throat plate. That is, as shown in FIG. 16, in the case where the left basic line is set for an inverse pattern, the needle N drops on the left side of the needle drop hole NB1 of the throat plate NB, thus interfering with the latter NB. As a result, the needle may be broken, or the throat plate NB may be damaged.
Furthermore, if, in the case where the right or left basic line is set, the drop position of the sewing needle N is greatly shifted from that of the needle in the case where the middle basic line is set, then sometimes the sewing machine shutter is unable to catch the upper thread passed through the sewing needle, so that tying the upper and lower threads together may be unsatisfactory.
This difficulty is due to the following fact: In the case where a basic line other than the middle basic line is selected, it is unnecessary to set the inverse pattern sewing mode, and therefore the shuttle and the needle drop hole NB1 are designed for the case only in which the middle basic line is set. Hence, the above-described difficulty may be eliminated by designing the shuttle and the needle drop hole with the case taken into account in which a basic line other than the middle basic line is set.
However, in this case, it is necessary to make the needle drop hole relatively larger, which gives rise to another problem that, during sewing, the large needle drop hole makes the work unstable, or it may catch the work. In addition, it is necessary to provide a relatively large shuttle. It is rather difficult to accommodate the large shuttle below the throat plate. In addition, it is necessary to design a new shuttle turning mechanism, which incurs great expense. Thus, to do so is considerably difficult.
As is apparent from the above description, the conventional zigzag sewing machine is not free from the difficulty that the right or left basic line and the inverse pattern sewing mode are set in error, so that the sewing needle is broken or the resultant seam is unsatisfactory. This is one of the factors which greatly impede the realization of a general purpose zigzag sewing machine.